1,721,040 research outputs found
The role of dispersal in population dynamics of breeding Ross's geese
Full text linkSpatial variation in density of organisms can lead to challenges in estimation of population size. Associated vital rates responsible for this variation also may vary geographically and in response to local ecological conditions, with the result that subunits of a metapopulation may have different trajectories. Both temporal and spatial variation in population size occurs not only as a result of additions through birth and deletions through death, but also from gains and losses arising from immigration and emigration, respectively. Although virtually all organisms have evolved mechanisms for dispersal, the role of movement in population dynamics has received far less attention than have contributions from recruitment and losses to mortality. I used mark-recapture techniques to make inferences about the role of movement in local population dynamics of Ross’s Goose (Chen rossii) colonies by estimating rates of movement between breeding subpopulations in the Queen Maud Gulf metapopulation. I also assessed decision-based philopatry (i.e., the role of previous nesting outcome; sensu Hoover 2003) and a potential cost of reproduction to female geese through experimental manipulation of nesting success. Previous nest fate influenced intra-colony dispersal as failed nesters moved further between consecutive nest sites, but inter-colony movement was not affected by previous nest fate. Regardless of previous nest fate, Ross’s Geese did not exhibit philopatry to nest sites, or to breeding territories, suggesting that philopatry occurs at a larger spatial scale. Breeding success accounted for a detectable, but only small amount of variation
Comparative reproductive strategies between long-tailed ducks and king eiders at Karrak Lake, Nunavut: use of energy resources during the nesting season
Full text linkEnergy demands can be particularly high in arctic-nesting birds that face harsh, unpredictable conditions during the breeding season. Consequences of these demands, particularly energy-partitioning during egg laying and incubation, are fundamentally important for arctic nesters. This study investigated differences in breeding strategies between Long-tailed Duck (Clangula hyemalis) and King Eider (Somateria spectabilis) in the central Canadian arctic. The focus was on ecological variables and influences of variation in nutrient resources used during incubation and egg production. Research was done at Karrak Lake, Nunavut, where both species nest sympatrically at relatively high densities, permitting comparative research about breeding strategies.This study used stable-carbon (d13C) and nitrogen (d15N) isotope analysis to investigate origins and allocation of endogenous (stored) and exogenous (external) nutrients used in egg production. Remote temperature sensors were placed in nests to estimate and compare incubation rhythms and gain insight into capital and income incubating strategies of both species. Results suggest that breeding Long-tailed Ducks and King Eiders used a “mixed” breeding strategy, that is they relied on both exogenous and endogenous resources for reproduction. Close correspondence between d13C and d15N values of egg components and potential diet items indicated that King Eiders allocated exogenous nutrients for egg production (albumen 98.1%, yolk protein 96.8%, whole yolk 98.4%, and yolk lipids 84%). Female King Eiders relied on endogenous nutrients for incubation, as evidenced by high incubation constancy (96%). Conversely, the range of d13C values in components of Long-tailed Duck eggs and d13C values of diet items suggested that although some females allocated endogenous reserves for egg production, most females allocated exogenous resources for egg production (albumen 98.5%, yolk protein 78.3%, whole yolk 84.9%, and yolk lipids 38.3%). Long-tailed Duck females had an 84% incubation constancy, suggesting less reliance on endogenous nutrients for incubation than was estimated for female King Eiders. Knowledge about the relative importance of endogenous reserves and exogenous nutrients for egg production and incubation may help direct management decisions to specific winter/staging and or breeding areas used by King Eiders and Long-tailed Ducks
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Parasite-host interactions in an arctic goose colony
Full text linkThe arctic is currently experiencing some of the greatest rates of warming. Newly emerging diseases in the arctic are of particular interest due to the implications these may have at southern latitudes if temperatures continue to rise around the globe. It is important to document changes in pathogen populations, such as alterations in range, virulence, prevalence, and abundance, and the effect these may have on their host populations. Parasites influence the reproductive success of their hosts in some cases. Studies on impacts of ectoparasites on avian reproductive success have generally been focused on species with altricial young. I studied the abundance of an apparently newly emerging nest-parasite and the effects of this parasite on Ross’s (Chen rossii) and lesser snow goose (Chen caerulescens caerulescens) reproductive success in the Karrak Lake goose colony, Nunavut, Canada from 2001 to 2004. The nest parasite, identified as the flea Ceratophyllus vagabundus vagabundus, was associated with goose eggs covered with spots of blood. The proportion of goose egg-shells covered by blood was positively correlated with flea abundance in the nest. This relationship allowed the use egg blood-coverage as an index of flea abundance for remaining analyses. Flea abundance in goose nests was associated with variables associated with the host and the host’s habitat. I used general linear models in conjunction with Akaike’s information criterion (AIC) to determine which factors were most important in influencing flea abundance in goose nests. The most parsimonious model to explain the relationship between egg blood coverage and flea abundance in goose nests included goose clutch size, age of nest bowl (new vs. old), history of nesting by geese on a specific plot within the colony, habitat within 0.5m of nest, and year. The best predictor of flea abundance was the age of the nest bowl, with nest bowls re-used by geese containing more fleas than new bowls. This relationship was expected as fleas over-wintered in goose nests at the Karrak Lake colony.
Logistic regression and AIC were used to determine whether egg blood-coverage was an important variable influencing nest success. All top five models included blood-coverage. Goose nest success was negatively influenced by fleas in most years. There was a threshold of egg blood-coverage at which nest success was affected, and this threshold varied, with >20% blood indicating a significant decline in nest success in two years, and >5% blood-coverage indicating a decrease in nest success in one year. To my knowledge, this is the first study that has examined the parasites of avian nests in an arctic ecosystem and was also the first to investigate the effect of nest parasites on birds with precocial young. More research is needed to determine what factors limit this flea population and whether fleas may become a regulating factor for geese in the Karrak Lake colony
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Neonate reserves, growth and survival of Ross' and Lesser Snow Goose goslings
Full text linkThe influence of egg size and brood dispersal on gosling growth and survival was studied in Ross' and Lesser Snow Geese hatched at Karrak Lake, N.W.T. Variation in neonate composition can influence growth, energetics and, possibly, subsequent dispersal patterns of young. Therefore, the relative nutrient profile and physiological development level of neonates in these two dimorphic species were examined by analyzing egg and gosling composition for seasonal, egg size and species-specific effects. Late laid eggs had less yolk protein and, in Ross' Geese, produced goslings with smaller pectoralis muscles. Since skeletal muscles are important for thermogenesis, this seasonal variation in muscle tissue may influence thermoregulatory abilities of late-hatched young. Egg composition varied isometrically with egg size. However, goslings from larger eggs were relatively smaller for their egg size yet contained the same relative nutrient content as goslings from smaller eggs. Because of their higher lipid:body size ratio, goslings from larger eggs were in better condition. Thus larger egg size may give an initial energetic advantage to goslings during periods of nutritional or thermal stress. Although no interspecific variation was observed for egg components, Ross' Goose goslings hatched with more protein for their egg size and larger gizzards for their body size. In addition, Ross' Goose goslings had less water per gram of lean dry mass than did Snow Goose goslings which indicates a greater functional maturity of Ross' Goose neonate tissue. Digestive efficiency, thermoregulatory ability and locomotor capacity may be relatively better in Ross' Geese and these characteristics may represent adaptations to metabolic constraints associated with smaller neonate
body size and foraging requirements.
Resource depletion around large nesting colonies may influence brood movements and subsequent growth and survival of nidifugous young. If per capita food availability increased with distance from the colony, then I predicted that broods settling farther from natal colonies should produce structurally larger and/or relatively heavier goslings than those broods feeding locally. I used radio telemetry to recapture marked broods and found indirect evidence of a nutrient gradient around the Karrak Lake colony. Broods dispersed 8-59 km away from Karrak Lake with Ross' Geese travelling farther than Snow Geese (19-59 km vs 8-21 km, respectively). These dispersal patterns may be a function of parental behavior, body size, bill morphology and nutrient requirements. For known age Ross' Goose goslings, birds reared farther from the colony were heavier for their body size than were goslings raised nearer to Karrak Lake. Body size varied randomly with distance in this sample. Both body size and condition varied positively with distance for Ross' and Snow Goose goslings of unknown age which were measured at marked brood recapture sites. A similar pattern was observed for body size in unmarked adults and this similarity may reflect common environmental effects during the growth period of adults and goslings. Although I found no distance effect on gosling survival, egg size was a significant determinant of within- (Snow and, possibly, Ross' Geese) and among-brood survival (Ross' Geese). Because goslings raised closer to the colony may fledge in poorer condition and thus may have lower first year survival, female philopatry to brood-rearing areas could indirectly influence parental fitness
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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